1. Field of the Invention
This invention generally relates to an electromagnetic clutch, such as for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automobile air conditioning system, and more particularly, to the structure of an electromagnetic coil assembly of the electromagnetic clutch.
2. Description of The Prior Art
An electromagnetic clutch for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automobile air conditioning system is illustrated in U.S. Pat. No. 4,799,578 to Matsushita. As illustrated in 578' Patent, the electromagnetic clutch includes an electromagnetic coil assembly comprising an annular magnetic housing having a U-shaped cross section in order to contain an annular electromagnetic coil which supplies magnetic flux for attracting an armature plate to an axial end plate portion of a rotor, and an annular supporting plate on which the annular magnetic housing is firmly fixed by, for example, spot welding. The annular supporting plate is firmly secured to the axial end surface of compressor housing by a plurality of rivets.
The electromagnetic coil is intermittently activated in response to automobile air conditioning demand, thereby intermittently supplying the magnetic flux for intermittently attracting the armature plate to the axial end plate portion of the rotor. Accordingly, power of the automobile engine is intermittently transmitted to the refrigerant compressor through the electromagnetic clutch in response to automobile air conditioning demand.
In order to generate the magnetic flux, the electromagnetic coil must be supplied DC electric power from a battery mounted in an automobile engine compartment, through a wire, although the battery and wire are not illustrated in the drawings of '578 Patent. Therefore, the wire which leads from the electromagnetic coil assembly to the outside of the electromagnetic coil assembly should be considered part of the structure.
One prior art embodiment regarding the above-mentioned structure is illustrated in FIGS. 1 and 2. Referring to FIGS. 1 and 2, electromagnetic coil assembly 100' of an electromagnetic clutch includes annular magnetic housing 110 having a U-shaped cross section, electromagnetic coil 120 contained within annular magnetic housing 110 and annular supporting plate 130 to which annular magnetic housing 110 is firmly fixed by, for example, spot welding. Annular magnetic housing 110 includes inner annular cylindrical portion 111, outer annular cylindrical portion 112 and annular bottom end portion 113 connecting one end of inner and outer annular cylindrical portions 111, 112. Annular supporting plate 130 is firmly secured to the axial end surface of compressor housing (not shown) by a plurality of rivets (not shown). The thickness of inner annular cylindrical portion 111 of housing 110 is designed to be slightly greater than the thickness of outer annular cylindrical portion 112 of housing 110. Hole 114 is formed at a certain region of bottom end portion 113 of annular magnetic housing 110. Spot facing 115 concentric with hole 114 is formed at bottom end portion 113 by using cutting tool 400 as shown in FIG. 4. Bottom surface 115 a of spot facing 115 is slightly slanted toward a center thereof. Consequently, annular flange 116 inwardly extending from inner side wall 115b of spot facing 115 is formed at the certain region of bottom end portion 113 of annular magnetic housing 110.
Grommet 140 is made of an elastomeric insulating material, for example, rubber, and penetrates through hole 114. Grommet 140 includes upper cylindrical portion 141, lower cylindrical portion 142 connected to a bottom end of upper cylindrical portion 142 and truncated corn-shaped portion 143 connected to a bottom end of lower cylindrical portion 142. Hole 144 is centrally and axially bored though grommet 140 and annular groove 145 is formed at a boundary between upper cylindrical portion 141 and lower cylindrical portion 142 of grommet 140. A diameter of upper cylindrical portion 141 is designed to be greater than a diameter of lower cylindrical portion 142. Annular upper surface 145b of groove 145 is slightly slanted so as to be along bottom surface 115a of spot facing 115. A diameter of annular bottom surface 145a of groove 145 is designed to be slightly greater than a diameter of hole 114. A diameter of upper cylindrical portion 141 of grommet 140 is designed to be slightly greater than a diameter of inner side wall 115b of spot facing 115. Accordingly, by utilizing elasticity of the rubber member, upper cylindrical portion 141 of grommet 140 is snugly disposed within spot facing 115 and annular groove 115 of grommet 140 is snugly engaged with annular flange 116.
Annular supporting plate 130 includes shallow cup-shaped region 130a defining indent 131 at its upper side and annular region 130b radially extending from a periphery of shallow cup-shaped region 130a. Annular supporting plate 130 is provided with semicircular cut-out portion 131a formed at annular region 130b thereof. Semicircular cut-out portion 131a is aligned with hole 114 to accommodate lower cylindrical portion 142 of grommet 140 therein when bottom end portion 113 of annular magnetic housing 110 is firmly fixed to annular region 130b of annular supporting plate 130. Annular magnetic housing 110 is firmly fixed to annular region 131a of annular supporting plate 130 by spot welding, thereby forming a plurality of spot welding traces 132 as shown in FIG. 1.
Annular flange 116 and semicircular cut-out portion 131a constitute engaging mechanism 200' which can engage with annular groove 145 of grommet 140.
Hole 144 of grommet 140 includes truncated cone-shaped section 144a at its upper side and cylindrical section 144b at its lower side. Truncated cone-shaped section 144a gradually narrows downwardly and is connected to cylindrical section 144b at its bottom end.
Cavity 110a defined by annular magnetic housing 110 and grommet 140 is filled with the heated epoxy resin 150, which is hardened by elapsing time with cooling, so as to fixedly dispose coil 120 therewithin.
As shown in FIG. 1, a pair of tiny identical projections 160 are formed at a bottom end surface of annular supporting plate 130 so as to be received within a pair of tiny identical indents (not shown) formed at the axial end surface of the refrigerant compressor housing to prevent rotational movement of electromagnetic coil assembly 100'.
Wire 170 leading from a bottom end portion of electromagnetic coil 120 snugly penetrates through hole 144 of grommet 140. Terminal end 171 of wire 170 is connected to plug 180 which is connected to a terminal end of another wire (not shown) leading from a control apparatus (not shown) of an automobile air conditioning system.
Accordingly, grommet 140 is used as an insulator, as a plug which can prevent leakage of the heated epoxy resin 150 through hole 114 from the inside of housing 110 and as a holder which can firmly hold wire 170.
By virtue of operation of the control apparatus of the automobile air conditioning system, electromagnetic coil 120 is intermittently activated in response to the automobile air conditioning demand. Therefore, power of the automobile engine is intermittently transmitted to the refrigerant compressor through the electromagnetic clutch in response to the automobile air conditioning demand.
Engaging mechanism 200' is formed as follows. First, referring to FIGS. 3 and 4, hole 114 is formed at bottom end portion 113 of annular magnetic housing 110 by punching out during press working of housing 110. Then, referring to FIGS. 4 and 5, spot facing 115 concentric with hole 114 is formed at bottom end portion 113 of annular magnetic housing 110 by using cutting tool 400. Consequently, annular flange 116 is formed at a bottom end surface of bottom end portion 113 of annular magnetic housing 110 as shown in FIG. 5. Next, referring to FIGS. 1 and 2, semicircular cut-out portion 131a is formed at annular region 130b of annular supporting plate 130 by punching out during press working of plate 130. Finally bottom end portion 113 of housing 110 is firmly fixed to annular region 130b of supporting plate 130 by spot welding with hole 114 aligned with semicircular cut-out portion 131a as shown in FIG. 1. Thus, engaging mechanism 200' is formed at the bottom end surface of bottom end portion 113 of annular magnetic housing 110 as shown in FIG. 2.
As described above, in this prior art embodiment, it is required not only to use the press but also to use cutting tool 400 of FIG. 4 in order to form engaging mechanism 200'. Therefore, a manufacturing process of electromagnetic coil assembly 100' of the electromagnetic clutch is complicated.